Stencil and method of making the same



April 1, 1969 E. F. BRENNAN ET 3,435,758

STENCIL AND METHOD OF MAKING THE SAME Filed March 2, 1966 FIG. 2

FIG. 3

lnve mors EDMUND E BRENNAN JOHN A. HAWES y J WflQMWM & 94/.

ATTYS.

United States Patent Office Patented Apr. 1, 1969 3,435,758 STENCIL AND METHOD OF MAKING THE SAME Edmund F. Brennan, Arlington, and John A. Hawes, Boston, Mass., assignors to Dymo Industries, Inc., Berkeley, Calif., a corporation of California Filed Mar. 2, 1966, Ser. No. 531,199 Int. Cl. B411 13/00; B41c 1/14; B32b 7/00 US. Cl. 101-1271 23 Claims ABSTRACT OF THE DISCLOSURE There is disclosed a stencil used on addressing machines, the stencil comprising a frame including a support member having a window therein, a layer of thermoplastic resin such as polyethylene resin on one surface of the support member around the window, an open lace-like base sheet formed of interlaced fibers, preferably a mixture of vegetable fibers and polyester fibers, covering the window on the side of the support member carrying the resin coating, the fibers of the base sheet around the periphery thereof being embedded in the resin coating to mount the base sheet in covering relationship with the window, a coating carried by the base sheet and comprising from about 13% to about 25% by weight of cellulose acetate resin, about 1.5% to about 9% by weight of modifying resins such as ethyl cellulose, nitrocellulose, cellulose acetate butyrate, cellulose acetate propionate and cellulose propionate, from about 35% to about 55% by weight of primary solvent plasticizers for the coating resins such as di-esters of phthalic acid, and from about 15% to about 40% by weight of secondary non-solvent plasticizers for the coating resins such as triaryl phosphates; there further is disclosed a method of mounting the stencil base sheet on the improved frame and specifically on the support member carrying the thermoplastic resin coating.

The present invention relates to stencils, and particularly to stencils for use on addressing machines, and specifically to coating compositions for the stencil and to stencil structures and to methods of making stencils.

Although the stencils of the present invention have general utility, certain important advantages thereof are more fully realized when the stencils are used on an addressing machine. Stencils for use on addressing machines must meet certain highl specialized requirements, namely, the stencil must be capable of being out by a typewriter utilizing the usual typing pressures or range of cutting force, the stencil must be capable of withstanding chemical attack from the inks utilized and after storage for several months must produce a good imprint the first time that ink is applied thereto under the usual printing pressures, and finally the stencil must be capable of giving a large number of impressions under the above-described conditions over a long useful life.

Heretofore so-called gelatin stencils have been used on addressing machines, the gelatin stencil consisting of a chemically hardened gelatin coating (typically hardened with dichromate) which has been plasticized with gly'cerine or other suitable plasticizers, the coating being applied from a water solution onto an open lacelike paper base. In order to cut an address on a gelatin stencil, it is first necessary to moisten the stencil with water after which the stencil is placed in a typewriter and the address typed thereon; the moistening operation swells the gelatin and weakens the bonds between the gelatin macromolecules, thus softening the coating to a point where it is easily cut with normal typing pressures; thereafter the stencil is allowed to dry (drying for twenty-four hours being typically recommended) before inking. Such a stencil can be inked, filed away for a period of weeks or months, and when used again will yield a good impression the first time that ink is applied therethrough. Such stencils are highly satisfactory in use-but do require wetting before cutting of the stencil on a typewriter.

Ordinary mimeograph stencils available heretofore are not suitable for use on addressing machines, such mimeograph stencils normally consisting of a highly plasticized and extended nitrocellulose coating on an open lace-like paper base. Although such a stencil does not require moistening before typing thereon, whereby to avoid the primary objection to the gelatin stencil, the mimeograph stencil will not stand up to the punishment of an addressing machine. Furthermore, the mimeograph stencil will not give a good first print after an extended period of storage.

Accordingly, it is an important object of the present invention to provide an improved stencil particularly adapted for use on addressing machines.

In connection with the foregoing object, it is more specifically an object of the invention to provide an improved stencil that can be cut on any typewriter with no wetting or moistening thereof, the stencil being capable of being cut in the normal cutting or typing range; more specifically, the improved stencil can be cut both at the low end of the cutting range to provide an adequate character thereon and at the high end of the "cutting range without being subject to chopping at the higher cutting pressures (chopping being the cutting of fully surrounded areas of the stencil such as in the letter 0 or in the letter p so as to remove such areas from the stencil).

Another object of the invention is to provide an improved stencil of the type set forth which will withstand the forces applied by an addressing machine, and which more particularly can withstand the printing pressures on the order of psi. to p.s.i., and further can be utilized a large number of times without substantial deterioration thereof.

Yet another object of the invention is to provide an improved stencil of the type set forth which after being used for printing can be stored for long periods of time up to as much as a year or more and still will print the first time without priming and with the application of the normal printing pressures thereto.

Still another object of the invention is to provide a stencil of the type set forth carrying a coating comprising a highly plasticized resin system coated on an open lace-like sheet, the ratio by weight of the plasticizers to the resins being in the range from about 2.0 to about 4.0.

Yet another object of the invention is to provide a coating for stencils of the type set forth, the coating having the required properties of dry cutting, durability, uncut shelf life, and the ability to print the first time without priming after storage, whereby to render the stencil incorporating the coating particularly useful on addressing machines.

A further object of the invention is to provide an improved stencil of the type set forth including a frame with a window therein having a support surface extending into the window and around the periphery thereof, the support surface having a thermoplastic resin coating thereon in which are imbedded the fibers at the periphery of the associated base sheet to mount the base sheet upon the frame.

In connection with the foregoing object, another object of the invention is to provide an improved stencil of the type set forth wherein the base sheet is mounted upon the frame by heat sealing the periphery thereof to the frame by means of a thermoplastic resin, therebyto increase the shelf like and the printability retention of the stencil.

A still further object of the invention is to provide a method of mounting a stencil base sheet on a frame therefor to produce the structure set forth in the foregoing object.

Further features of the invention pertain to the compositions of the coatings and to the particular arrangement of the parts and to the particular arrangement of the steps of the method, whereby the above-outlined and additional operating features thereof are attained.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawing, in which:

FIG. 1 is a perspective view of a stencil made in accordance with and embodying the principles of the present invention;

FIG. 2 is a much enlarged view in vertical section through the stencil of FIG. 1 along the line 22 thereof; and

FIG. 3 is a diagrammatic view illustrating the manner of mounting the base sheet on the frame thereof for the stencil of FIG. 1.

Referring to FIG. 1 of the drawing, there is illustrated a stencil made in accordance with and embodying the principles of the present invention, the stencil 10 comprising the usual frame having a window therein covered by a base sheet 70 carrying a stencil coating 80 therein and therethrough. More specifically, the frame 20 comprises a lower frame member having the corners thereof slightly rounded and generally rectangular in shape except for the area in the indexing notch 21 (see FIG. 1). Formed centrally of the frame member 30 is a generally rectangular opening 32. An upper frame member is also provided having a generally rectangular outer periphery identical in shape to the outer periphery of the frame member 30, the frame member 40 having a generally rectangular opening 42 disposed centrally thereof, the dimensions of the opening 42 being slightly greater than those of the opening 32 as may be best seen from FIG. 2. Finally, there is disposed between the frame members 30 and 40 a paper support member 50 having an outer periphery generally rectangular in shape and having the same shape as the outer periphery of the frame members 30 and 40, there being formed in the support member 50 a generally rectangular opening 52 having dimensions slightly less than thoseof the opening 32 and defining the window for the frame 20. Provided on the upper surface of the support member 50 is a resin layer 60, preferably formed of polyethylene resin, and completely covering the upper surface of the support member 50. The frame member 30 and the frame member 40 and the support member 50 are all mutually secured together such as by adhesive as illustrated in FIG. 2 to provide the frame member 20 having a window therein defined by the periphery of the opening 52 in the support member 50.

Overlying the window in the frame 20 is the base sheet 70, the base sheet 70 being generally rectangular in shape and lying upon the upper surface of the support member 50, the outer edges of the base sheet 70 extending well onto the upper surface of the support member 50. In accordance with the present invention, the fibers of the base sheet 70 such as the fibers 71 in FIG. 2 are imbedded in and thereby secured to the resin coating 60, thereby to mount the base sheet 70 upon the support member 50 completely around the periphery of the base sheet 70. Finally, there is provided on the base sheet 70 a novel stencil coating made in accordance with and embodying the principles of the present invention, the coating 80 being of uniform character and being disposed throughout the volume of the base sheet 70.

In a typical constructional example of the stencil 10, the frame 20 has a length of 4 /2 inches and a width of 2 inches; the window therein has a length of 3 /2 inches and a width of one inch; the frame members 30 and 40 have a thickness each of 20 mils, the support member 50 has a thickness of 7 mils and the resin coating 60 has a thickness of 1 mil. The frame members 30 and 40 and the support member 50 are preferably formed of a good grade cardboard, and the resin coating 60 is a polyethylene resin as has been pointed out above. The base sheet 70 is of open lace-like structure as is common in the art and may be formed of vegetable fibers such as abaca (Manila hemp) or kozo fiber (imported from Japan). In accordance with one preferred example of the present invention, the base sheet 70 is formed of a mixture of vegetable fibers and polyester resin fibers, the preferred polyester resin being that sold under the trademark Dacron; in the paper comprising the mixture of vegetable and polyester fibers, the polyester fibers may comprise as little as 5% by weight of the mixture up to as much as 50% by weight or more of the mixture, the preferred composition being 25% by weight polyester fiber and 75% abaca fibers, such a paper being that sold under the trademark Dexstar 630 by Dexter Paper Company. It has been found that the addition of the polyester resin renders the base sheet 70' particularly resistant to chopping thereof when certain characters such as the letter 0 are typed thereon using high typing pressures. Other synthetic organic resin fibers may be used in place of the polyester resin fibers, illustrative examples being cellulose triacetate resin fibers sold under the trademark Fortisan, polyacrylonitrile resin fibers sold under the the trademark Orlon, and polyamide resin fibers.

The following are specific examples of the improved coating 80 of the present invention, it being understood that these examples are illustrative and are not set forth to limit the scope of the invention.

EXAMPLE 1 A coating composition was formulated containing the following ingredients:

Ingredient: Percent by weight Cellulose acetate 18.1 Ethyl cellulose 3.6 Di(methoxy ethyl) phthalate 47.1 Triphenyl phosphate 31.2

These ingredients were dissolved in a mixture comprising by weight 60% acetone and 40% methyl ethyl ketone, there being 34% of the solid ingredients present in the mixture. The composition was then impregnated in the base sheet material comprising 25 by weight polyester fibers and 75% by weight abaca fibers and the solvents removed by evaporation to provide 3.1 pounds of dry solids .per pound of base sheet material. The base sheet material was then cut to provide the desired size of base sheets 70. a

The base sheet 70 cut to size was then placed upon the upper surface of the frame 20 in registration with the opening 52 in the support member 50 (see FIG. 3),

whereby the periphery of the base sheet 70 overlay the polyethylene resin coating 60. A sealing head 90 was provided having an outer periphery generally rectangular in shape and having dimensions only slightly less than those of the base sheet 70 and having an opening therein with dimensions slightly greater than those of the opening 52, whereby to provide an annular Work surface 91 completely around the periphery of the base sheet 70 and overlying only the marginal portions thereof. In accordance with the invention, the sealing head 90 was heated to a temperature of 395 F. and then pressed against the upper surface of the base sheet 70 for 0.4 second at an applied pressure of 50 psi. and thereafter removed. Such pressing of the sealing head 90 against the parts of the stencil serves to imbed the fibers 71 in the polyethylene resin coating 60 as illustrated in FIG. 2, thereby firmly to mount the base sheet 70 upon the support member 50 and thence upon the frame 20 in the overlying and covering relationship with the window therein; the stencil 10 is then cooled to room temperature.

The resultant stencil 10 was then placed in a typewriter and letters cut thereon as illustrated at 72 in FIG. 2, the stencil 10 being typed upon while in the dry condition with no pre-treatment whatsoever. The typing pressure utilized was in the mid-range of intensity and served to displace a portion of the coating 80 as is diagrammatically illustrated at 81 in FIG. 2, thus to expose a portion 72 of the base sheet 70, the exposed portion 72 constituting the typed character. The stencil 20 was then placed in an addressing machine and addressing machine ink forced therethrough at a pressure of 140 p.s.i. to print a label in the usual manner, the ink passing through the exposed portion 72 of the base sheet 70, it being understood that the coating 80 elfectively blocks passage of ink through the associated unexposed portions of the base sheet 70. The stencil 10 was then stored without any special treatment, and it was found that the stencil 10 had the ability to print without priming after extended periods of storage on the order of twelve months or more. Furthermore, the stencil 10 was found to be very durable, several hundred or even several thousand satisfactory prints being made therefrom over a substantial period of time, all without the necessity for priming after each storage period; in other words, the stencil 10 exhibited good printability retention. Finally, other stencils 10 made in accordance with Example 1 were stored in the uncut condition, and after even extended periods of storage on the order of twelve months or more, it was found that the stencil 10 could be readily cut without any wetting or other preparation thereof on the usual typewriter in the usual cutting pressure range and still exhibited good characteristics of durability and printability retention, i.e., the ability to print the first time without priming even after extended storage.

The cellulose acetate in the composition of Example 1 is in the main resin body, one preferred example of a suitable cellulose acetate being that sold under the trademark E398-10 by the Eastman Chemical Company, this product having 39.8% acetyl content. Other suitable cellulose acetate compositions of varying acetyl content and of varying viscosities may be substituted, another specific example being that sold under the trademark E395-3 by the Eastman Chemical Company. Cellulose acetate is unusually well suited for the coating composition of Example 1 since it is oil resistant and more polar than most resins and can carry addressing machine inks for months without being adversely affected thereby. The amount of cellulose acetate in the composition of Example 1 can vary fiom as little as 13% by weight thereof to as much as 25% by weight thereof.

The ethyl cellulose in the composition of Example 1 is a modifying resin which is incorporated therein to provide for better processing and to provide a coating having low tack. Ethyl cellulose also provides for low migration of plasticizers to the surface giving a drier feeling sheet 70 and slows down migration of the plasticizers to any contacting surface such as the stencil frame thus improving shelf life and printability retention; in addition, the ethyl cellulose tends to counteract chopping during the typing operation and increases the typing pressure range, improving the sensitivity at the low end of the typing pressure range and preventing chopping at the high end of the typing pressure range. Preferably the amount of modifying resin such as ethyl cellulose useful in the invention is in the range from about 1.5% to about 9% by weight; too much modifying resin such as ethyl cellulose causing the resulting coating to be too weak and to lose its print retention characteristics. When ethyl cellulose is utilized as a modifying resin, a preferred type is that sold by Hercules Powder Company under the designation N10, other suitable grades being those designated N4, N7, N22, N50, and N100. In general the derivatives of cellulose are preferred as modifying resins, those particularly useful in the present invention being ethyl cellulose, cellulose acetate butyrate, cellulose propionate, nitrocellulose, and cellulose acetate propionate; when nitrocellulose is utilized as a modifying resin, those sold under the designations RS 15-20 sec and RS /2 second are particularly useful; when the cellulose acetate butyrate is utilized as a modifying resin, it is preferred that there be a butyryl content of 38% by weight, for example one sold by Eastman Chemical Company under the designation EAB 381-20 is useful; when cellulose propionate is used, one sold under the designation PLFS- 70 is useful; and a useful example of cellulose acetate propionate is that sold under the designation EAP 482- 20 by Eastman Chemical Company. In Example 1, the ratio between the main resin body of cellulose acetate and the modifying resin, ethyl cellulose, is approximately 5:1; this ratio can vary from as little as 2:1 to as much as.11:1, a smaller ratio causing the stencil coating to be too weak and to lose the printability retention capabilities thereof, and a larger ratio causing the stencil coating to be oily, to have a narrow typing range, poor printability retention and to be tacky.

The di(methoxy ethyl) phthalate (di(2-methoxyethyl) phthalate) in the composition of Example 1 is a primary plasticizer, and more specifically is a solvent plasticizer for the resin composition. The plasticizer must be resistant to the addressing machine inks, must have a low volatility, must exhibit resistance to migration, must impart flexibility and softening to the resin composition without producing excessive tack therein. In the composition of Example 1, the primary solvent plasticizer, namely, the di(-methoxy ethyl) phthalate may vary from about 35% to about 55% by weight of the solids content thereof. Other suitable primary plasticizers are other di-esters of phthalic acid such as ethyl phthalyl ethyl glycolate and di(ethoxy ethyl)phthalate.

The triphenyl phosphate in the composition of Example 1 is a secondary plasticizer, and more specifically, a nonsolvent plasticizer for the resin system. The presence of secondary plasticizers tends to give better sensitivity and lower tack in the coating and may be present in an amount from about 15% to about 40% by weight of the composition, further provided that the primary plasticizers are always present in amounts greater than the secondary plasticizers as set forth more fully hereinbelow. In general the suitable secondary plasticizers are the triaryl phosphates, other examples of suitable secondary plasticizers being cresyl diphenyl phosphate, tricresyl phosphate and tritolyl phosphate.

It will be understood that other suitable solvents may be used in applying the coating to the base sheet and that other proportions between the acetone and the methyl ethyl ketone may be used in the preferred solvent system. Likewise the amount of solids in the coating composition can be varied from as little as 25 by weight up to as much as 50% by weight or more depending on the coating methodused and the coating solids desired. In addition the amount of solids deposited on the base sheet can be varied from as little as 2 pounds of coating solids per pound of base sheet up to as much as 3.5 pounds of coating solids per pound of base sheet or more.

From the above it will be seen that the composition of Example 1 is a highly plasticized resin system comprising a main resin plus modifying resins therefor, two types of plasticizers being utilized, namely, a primary solvent plasticizer for the resin system and a secondary non-solvent plasticizer for the resin system. In Example 1, the ratio by weight between the total plasticizers and the total resins in the compositions is 3.621, and it further has been found that the range can be varied from as little as 2.021 to as much as 4.0:1. At the lower ratio of plasticizers to resin, the typing pressure range is substantially narrowed, and conversely, at the high ratio of plasticizers to resin, the stencil coating looses its durability. It further has been found that the ratio between the primary plasticizers and the secondary plasticizers is also critical, the ratio preferably being in the range from about 1.2:1 to about 3.5:1, this ratio in Example 1 being about 1.5: 1. As the ratio of the primary plasticizers to the secondary plasticizers goes up, the coating becomes tackier and harder to process, but the print retention thereof is improved.

EXAMPLE 2 The process of Example 1 was repeated utilizing the following composition of the solids in the stencil coating:

Ingredient: Percent by weight Cellulose acetate 23 Ethyl cellulose Di(methoxy ethyl)phthalate 42 Triphenyl phosphate 30 In the above composition, the ratio of the plasticizers to the resins is approximately 2.6:1 and the ratio of the di(methoxy ethyl)phthalate to the triphenyl phosphate is approximately 1.4: 1. The resultant stencil when utilized on an addressing machine as described above with respect to Example 1 showed all of the desirable chracteristics described herein.

EXAMPLE 3 The process of Example 1 was repeated utilizing the following composition of the solids in the stencil coating:

Ingredient: Percent by weight Cellulose acetate 23 Ethyl cellulose 5 Di(methoxy ehtyl)phthalate 56 Triphenyl phosphate 16 Ingredient: Parts by weight Cellulose acetate 16.5 Ethyl cellulose 3.5 Di(methoxy ethyl)phthalate 61.5 Triphenyl phosphate 17.5

In the above composition, the ratio of the plasticizers to the resins is approximately 3.721 and the ratio of the di(methoxy ethyl) phthalate to the triphenyl phosphate is approximately 35:1. The resultant stencil when utilized on an addressing machine as described above with respect to Example 1 showed all of the desirable characteristics described therein.

EXAMPLE 5 The process of Example 1 was repeated utilizing the following composition of the solids in the stencil coating:

Ingredient: Parts by weight Cellulose acetate 16.5 Ethyl cellulose 3.5 Di(methoxy ethyl) phthalate 45.5 Triphenyl phosphate 33.5

In the above composition, the ratio of the plasticizers to the resins is approximately 3.7:1 and the ratio of the di(methoxy ethyl)phthalate to the triphenyl phosphate is approximately 1.4: 1.

As has been pointed out above, other modifying resins may be utilized in place of the ethyl cellulose illustrated in Example 1 above, the following being an illustration of the substitution of nitrocellulose resin therefor.

EXAMPLE 6 The process of Example 1 was repeated utilizing the following composition of the solids in the stencil coating:

Ingredient: Percent by weight Cellulose acetate 18.5 Nitrocellulose (RS /2 sec. Hercules) 3.7 Di(methoxy ethyl) phthalate 46.6 Triphenyl phosphate 31.2

The nitrocellulose utilized had a nitrogen content of 11.2% to 12.8% by weight. When the stencil made in accordance with Example 6 was utilized in an addressing machine in accordance with Example 1 described above, it was found that the stencil possessed all of the desirable characteristics noted. In fact the print retention was improved as was the durability, but the typing pressure range was slightly less than that for the stencil of Example 1.

EXAMPLE 7 The process of Example 6 was repeated and the composition was the same except that for the nitrocellulose thereof there was substituted cellulose acetate butyrate (CABSOO-l Eastman) in a like amount. The resultant stencil had properties substantially like those of the stencil of Example 6.

EXAMPLE 8 EXAMPLE 9 The process of Example 1 was repeated utilizing the following composition of the solids in the stencil coating:

Ingredient: Percent by weight Cellulose acetate 18.5 Ethyl cellulose 3.7 Di(methoxy ethyl)phthalate 46.6 Cresyl diphenyl phosphate 31.2

The resultant stencil possessed the desirable characteristics set forth above with respect to the stencil made in accordance with Example 1.

EXAMPLE 10 The process of Example 1 Was repeated utilizing the following composition of the solids in the stencil coating:

Ingredient: Percent by weight Cellulose acetate 18.5 Ethyl cellulose 3.7 Di(methoxy ethyl)phthalate 46.6 Triphenyl phosphate 20.8 Cresyl diphenyl phosphate 10.4

EXAMPLE 1 1 The process of Example 1 was repeated utilizing the following composition of the solids in the stencil coating:

Ingredient: Percent by weight Cellulose acetate 18.5 Cellulose acetate butyrate 3.7 Di(methoxy ethyl) phthalate 46.6 Triphenyl phosphate 20.8 Cresyl diphenyl phosphate 10.4

The resultant stencil possessed the desirable characteristics pointed out above with respect to the stencil of Example 1.

In each of Examples 10 and 11 above the cresyl diphenyl phosphate is a second secondary solvent, the cresyl diphenyl phosphate being of particular value during the processing of the stencil and in serving to render the product more tack free. The ratio between the triphenyl phos phate and the cresyl diphenyl phosphate is preferably in the range from about 1:1 to about 4:1, the ratio being 2:1 in Examples 10 and 11.

The following are examples of the use of other primary plasticizers in place of di(methoxy ethyl)phthalate.

EXAMPLE 12 The process of Example 1 was repeated but for the di(methoxy ethyl)phthalate there was substituted 47.1 parts by weight of ethyl phthalyl ethyl glycolate. The resultant stencil had all of the desirable properties pointed out both in respect to the stencil of Example 1.

EXAMPLE 13 The process of Example 1 was repeated but for the di(methoxy ethyl)phthalate there was substituted 47.1 parts by weight of diethoxy ethyl phthalate. The resultant stencil had all of the desirable properties pointed out both with respect to the stencil of Example 1.

It further is possible to utilize a mixture of modifying resins and a mixture of secondary solvents in the coating composition, the following being an example of a stencil made in this manner.

EXAMPLE 14 The process of Example 1 was repeated utilizing the followlng composition of the solvents in the stencil coating:

Ingredient: Percent by weight Cellulose acetate 20.4 Ethyl cellulose 2.0 Nitrocellulose (Ill-12.8% by weight nitrogen) 2.0 Di(methoxy ethyl)phthalate 45.6 Triphenyl phosphate 20.0 Cresyl diphenyl phosphate 10.0

The resultant stencil possessed all of the desirable characteristics set forth above with respect to the stencil of Example 1.

In the mounting of the base sheet 70 upon the support member 50, the processing temperature, time and pressure can be modified and still produce a satisfactory product. For example, the temperature of the sealing head 90 may vary from about 375 F. to about 420 F. The time of heating may vary from 0.2 second to about 1.0 second while the applied pressure may vary in the range from about 25 psi. to about p.s.i., it being understood that the heating time and heating pressure are reciprocally related, whereby shorter heating times require higher pressures and longer heating times require lesser pressures, for example, a heating time of aboupt 0.25 second requires pressure of 60 psi. Other resins may be substituted for the polyethylene resin in the coating 60, such resins being heat-sealable resins that are resistant to the plasticizers used in the coating 80 and that are resistant to the addressing machine inks that will be encountered in use, another specific example being polypropylene resins. Summarizing, the mounting of the base sheet 70 upon the support member 50 by means of the polyethylene resin coating 60 is highly advantageous as compared with adhesive bonding of the base sheet 70 upon the support 50- More specifically, the mounting by heat sealing of the resin layer 60 limits migration of the plasticizers from the coating 80 and the loss of printability retention and shelf life.

From the above it will be seen that there have been provided improved stencils including improved stencil coatings therefor and improved structures for mounting the base sheet on the frame as well as improved methods of making the stencil, and specifically an improved method of mounting the base sheet upon the frame which fulfill all of the objects and advantages set forth above. More particularly, there has been provided an improved stencil particularly adapted for use on addressing machines, the stencil being capable of being cut on any typewriter with no moistening or other special preparation thereof. The stencil furthermore is capable of being cut in a normal cutting or typewriting pressure range, there being good sensitivity at the low end of the typing pressure range and no chopping at the high end of the typing pressure range. Furthermore, the resultant stencil can Withstand the forces applied by an addressing machine, and more particularly can withstand the printing pressures on the order of p.s.i. to p.s.i., and has a high durability whereby it can be utilized a large number of times without substantial deterioration thereof. In addition the stencil after being used for printing can be stored for long periods of time up to as much as twelve months or more and still will print the first time Without priming and with the application of the normal printing pressures thereto. Finally, the stencil shows a long uncut shelf life.

There also has been provided an improved frame and structure for mounting the base sheet on the frame, the fibers in the periphery of the base sheet being imbedded in a resin layer on the associated surface of the support member. There further has been provided an improved method of mounting a stencil base sheet on the frame to produce the desired structure.

While there have been described what are at present considered to be certain preferred embodiments of the invention, it will be understood that various modifications may be made therein, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A coating composition for the base sheet of a stencil used on addressing machines, said composition comprising from about 13% to about 25% by weight of cellulose acetate resin, from about 1.5% to about 9% by weight of modifying resins, from about 35% to about 55% by weight of primary solvent plasticizers for said resins, and from about 15% to about 40% by weight of secondary non-solvent plasticizers for said resins, the ratio of weight of said primary plasticizers to said secondary plasticizers being in the range from about 1.2:1 to about 3.521.

2. The coating composition set forth in claim 1, wherein said cellulose acetate has an acetyl content of about 40%.

3. The coating composition set forth in claim 1, wherein said modifying resins are selected from the group consisting of ethylcellulose, nitrocellulose, cellulose acetate butyrate, cellulose acetate propionate, and cellulose propionate.

4. The coating composition set forth in claim 1, wherein said modifying resins comprise equal parts by Weight of ethyl cellulose and nitrocellulose.

5. The coating composition set forth in claim 1, wherein the ratio by weight of said plasticizers to said resins is in the range from about 2.0:1 to about 4.0:1.

6. The coating composition set forth in claim 1, where in said primary plasticizers are di-esters of phthalic acid.

7. The coating composition set forth in claim 6, wherein said primary plasticizers are selected from the group consisting of dimethoxy ethyl phthalate, ethyl phthalyl ethyl glyeolate and diethoxy ethyl phthalate.

8. The coating composition set forth in claim 1, wherein said secondary plasticizers are triaryl phosphates.

9. The coating composition set forth in claim 8, wherein said secondary plasticizers are selected from the group consisting of triphenyl phosphate, cresyl diphenyl phosphate, tricresyl phosphate and tritolyl phosphate.

10. The coating composition set forth in claim 9, wherein said secondary plasticizers are a mixture of triphenyl phosphate and cresyl diphenyl phosphate wherein the ratio by weight therebetween is in the range from about 1:1 to about 4:1.

11. The coating composition set forth in claim 1, and further comprising a solvent for said resins and said plasticizers to form a fiowable mixture thereof.

12. The coating composition set forth in claim 11, wherein said solvents are selected from the group consisting of acetone and methyl ethyl ketone, the resins and the plasticizers comprising from about 25% to about 50% by Weight of said mixture.

13. A stencil for use on addressing machines comprising, an open lace-like base sheet, and a coating on said base sheet comprising from about 13% to about 25% by weight of cellulose acetate resin, from about 1.5% to about 9% by weight of modifying resins, from about 35 to about 55% by weight of primary solvent plasticizers for said resins, and from about 15% to about 40% by weight of secondary non-solvent plasticizers for said resins, the ratio by weight of said primary plasticizers to said secondary plasticizers being in the range from about 1.211 to about 3.5:1.

14. The stencil set forth in claim 13, wherein said base sheet is a mixture of vegetable fibers.

15. The stencil set forth in claim 13, wherein said base sheet is a mixture of vegetable fibers and polyester fibers.

16. The stencil set forth in claim 13, wherein the ratio by weight of said plasticizers to said resins is in the range from about 2.0:1 to about 4.0: 1.

17. A stencil for use on addressing machines comprising a support member having a window therein, a layer of thermoplastic resin on at least one surface of said support member around the window therein, and an open lace-like base sheet formed of interlaced fibers carried by said support member and covering said window on the side of said support member carrying said thermoplastic resin coating, the fibers of said base sheet around the periphery thereof being imbedded in said thermoplastic resin coating to mount said base sheet in covering relationship with said window on said support member,

and a coating carried by said base s'heet, said coating comprising from about 13% to about 25% by weight of cellulose acetate resin, from about 1.5% to about 9% by weight of modifying resins, from about 35% to about 55% by weight of primary solvent plasticizers for said coating resins, and from about 15% to about 40% by weight of secondary non-solvent plasticizers for said coating resins, the ratio by weight of said primary plasticizers to said secondary plasticizers being in the range from about 1.2:1 to about 3.521, said thermoplastic resin coating on said support member being highly resistant to said primary solvent plasticizers and said secondary nonsolvent plasticizers for said coating resins.

18. The stencil as set forth in claim 17, wherein said thermoplastic resin is a polyethylene resin.

19. The stencil as set forth in claim 17, wherein said base sheet is a mixture of vegetable fibers.

20. The stencil as set forth in claim 17, wherein said base sheet is a mixture of vegetable fibers and polyester fibers.

21. The stencil as set forth in claim 17, wherein the ratio by weight of said plasticizers to said coating resins is in the range from about 2.0:1 to about 4.0:1.

22. A method of mounting a stencil base sheet on a frame therefor comprising providing a frame with a window therein having a support surface extending into the window and around the periphery thereof and carrying on one surface thereof a thermoplastic resin coating, providing a base sheet of interlaced fibers carrying thereon a coating comprising from about 13% to about 25% by weight of cellulose acetate resin, from about 1.5 to about 9% by weight of modifying resins, from about 35% to about 55% by weight of primary solvent plasticizers for said resins, and from about 15% to about 40% by weight of secondary non-solvent plasticizers for said resins, the ratio by weight of said primary plasticizers to said secondary plasticizers being in the range from about 1.2:1 to about 3.5:1; placing said base sheet of interlaced fibers in covering relationship on said window and having the periphery thereof disposed upon said resin coating, applying heat to said coating sufficient to render said resin plastic, pressing the fibers at the periphery of said base sheet into said plastic resin, and cooling said plastic resin to trap the fibers at the periphery of said base sheet therein to mount said base sheet upon said frame.

23. The method of mounting a stencil base sheet on a frame therefor as set forth in claim 22, wherein said resin is a polyethylene resin, and said thermoplastic resin coating is heated to a temperature in the range from about 375 F. to about 420 F. during a time interval from about 0.2 second to about 1.0 second and the fibers are pressed into said thermoplastic resin coating under pressure in the range from about 25 p.s.i. to about p.s.i.

References Cited UNITED STATES PATENTS 2,210,712 8/1940 Elliot 101127.1 1,792,095 2/ 1931 Horii 1 1735 .5 1,973,151 9/1934 Murphy 1011'28.2 2,693,426 11/1954 Hoover et al. 11735.5

FOREIGN PATENTS 718,839 3/1942 Germany.

DAVID KLEIN, Primary Examiner.

US. Cl. X.R. 

